Device for observing waveform repeated at high frequency

ABSTRACT

Apparatus for observing waveforms of extremely short duration and repeated at high frequencies wherein an electron beam is produced having a density variation corresponding to the waveform to be observed. The electron beam is deflected by a microwave voltage synchronized with the repetition rate of the waveform. A phase shifter under control of a saw-tooth generator sweeps the phase angle between the electron beam and the microwave voltage and the density of the electron beam is detected only at a predetermined deflection and displayed with the density corresponding to intensity and time corresponding to phase difference.

United States Patent 1 [111 3,900,759 Fujisawa Aug. 19, 1975 DEVICE FOROBSERVING WAVEFORM REPEATED AT HIGH FREQUENCY Primary Examiner--MaynardR. Wilbur [75} inventor: Kazuo Fujisawa, Osaka, Japan Asst-Slam EmmmerT'Blum [73] Assignee: Osaka University, Osaka, Japan [22] Filed: Mar. 14,1974 [2|] Appl. No.: 450,972

[ 5 7 1 ABSTRACT Apparatus for observing waveforms of extremely shortduration and repeated at high frequencies wherein an electron beam isproduced having a density variation Foreign Application Prioriiy Datacorresponding to the waveform to be observed. The

June 25,1973 Japan 48-71539 electron beam is deflected by a microwavevoltage synchronized with the repetition rate of the waveform.

[52] US. Cl 315/10; 328/231 A phase shifter under control ofa saw-toothgenerator [5|] Int. Cl. HOlj 31/26 sweeps the phase angle between theelectron beam [58] Field of Search 315/86. 9, l(), 371, 379, and themicrowave voltage and the density of the elec- 315/30, 393; 330/47;250/549, 207; 328/23l tron beam is detected only at a predetermineddeflection and displayed with the density corresponding to [56]References Cited intensity and time corresponding to phase difference.

UNITED STATES PATENTS 4 Cl Z Dra F' 3,268,860 8/1966 Wischmeyer 328/23]gums 7 16 r HMJZ K flflJf/EL .SH/FTEK DEVICE FOR OBSERVING WAVEFORMREPEATED AT HIGH FREQUENCY This invention relates to an improved devicefor observing a waveform of an extremely short duration repeated at highfrequency.

In order to observe a waveform of extremely short duration which isrepeated at high frequency, a sampling oscilloscope has been used. Inthis oscilloscope, a voltage pulse which is synchronized with thewaveform to be observed and varies its phase bit by bit at every cycle,is produced and the waveform is sampled during the duration of thispulse and amplified for use in waveform display. As the duration of thevoltage pulse must be short as compared with the duration of thewaveform to be observed, the shorter the duration of the waveformbecomes, the shorter the required duration of the voltage pulse becomes.Thus, the prior techniques only enable observation of the waveformshaving a duration of the order of a nanosecond at the best. With theadvance of the recent lasar technique, however, it has become possibleto produce pulses having durations of the order of picosecond and,consequently. it has become necessary to observe the pico second lightpulses.

Therefore, an object of this invention is to provide a novel andimproved device enabling display of a waveform having an extremely shortduration such as of the order of a picosecond and being repeated at ahigh frequency.

The device according to this invention comprises means for producing anelectron beam having a density variation according to the waveform to beobserved, means for deflecting said electron beam under control of amicrowave voltage which is synchronous with the repetition of saidwaveform to be observed, means for sweeping the phase difference betweensaid electron beam and microwave voltage at a low frequency, means forcontrolling said electron beam only at the position corresponding to apredetermined deflection effected by said deflecting means, and meansfor displaying the magnitude of the electron flow collected by saidcollecting means along the phenomenon axis and said phase differencealong the time axis.

Other features and operation of the device of this invention will bedescribed in more detail hereinunder with reference to the accompanyingdrawings.

In the drawings:

FIG. 1 is a schematic sectional side view, partly in block form,representing an embodiment of this invention for observing the waveformof a high frequency light pulse; and

FIG. 2 is a waveform diagram presented to aid the explanation of theoperation of the device of FIG. 1.

Referring to FIG. 1, a photoelectric surface 1 is formed on atransparent electrode (not shown) which is formed on the inner face ofone end wall of an evacuated glass envelope E, and arranged to receive alight pulse L to be observed. Located in front of the photoelectricsurface I are an anode electrode 2, lens forming electrodes 3, 4 and 5,a drift tube 6 and a reentrant cavity resonator 7 in that order. Thecavity resonator 7 is coupled to a waveguide 8 through a coupling hole12 and its inner post forms a modulation gap II in the center. Pin-holes9 and 10 are formed in the walls of the cavity along the tube axis. Atthe other end of the envelope E, there is a masking electrode I3 havinga pin-hole l4 and an electron collector electrode 15 is located behindthe pin-hole 14. The pin-hole 14 of the masking electrode 13 ispositioned a specific distance from the tube axis so that only theelectron beam encountering the corresponding deflection can pass thepin-hole 14 to be collected by the electrode 15.

A microwave oscillator 16 generating a proper microwave signal Psynchronized with the repetition of the light pulse L to be observed isconnected through a phase shifter 17 to the waveguide 8. A saw-toothwave generator 18 is connected to the drift tube 6 through a fixedcontact 19a of a single-pole doublethrow switch 19 and a transformer 20and also to the control terminal of the phase shifter 17 through theother fixed contact 19b of the switch 19. The output of the saw-toothwave generator 18 is further connected to the time axis input X of acathode-ray tube oscilloscope 23. The electron collector electrode 15 isgrounded through a resistor 21 and also connected through a high gainamplifier 22 of the phenomenon axis input Y of the oscillator 23.

Now, the operation of the device of FIG. 1 will be described with theaid of FIG. 2. The light pulse L incident upon the photoelectric surface1 emits an electron beam B having a density waveform which is identicalto the waveform of itself, as shown in FIG. 2 (l). The pulsed electronbeam 8 passes through the anode electrode 2, the lens electrodes 3, 4and 5 and the drift tube 6 and enters the cavity resonator 7 from thepin-hole 9. The oscillator 16 generates a microwave signal P,synchronous with the repetition of the pulsed electron beam B andaccordingly with the incident light pulse L, and the signal P is shiftedin phase by the phase shifter 17 and applied to the modulation gap 11 ofthe resonator 7 through the waveguide 8 as a microwave signal P, asshown in FIG. 2 (2). As an example, the period of the microwave signalP, is selected to be one third of the repetition period T of the pulsedbeam B in the drawing.

The electron beam B is deflected laterally in the modulation gap 1 l byan electric field controlled by the signal P, and comes out of thepinhole 10. Although most of the deflected electrons of the beam collideagainst the masking electrode 13 and are absorbed thereby, only theelectrons passing through the pinhole 14 are collected by the collectorelectrode 15. Assuming that the deflected portion of the electron beampassing through the pin-hole 14 corresponds to a voltage level V, of themicrowave signal P,, the possible time points at which the electron beampasses through the pin-hole 14 are t t as shown in FIG. 2(2) and, inthis case, an electron flow having a density 1, passes therethrough atthe time points t t,,. and is collected by the collector electrode 15 toinduce a voltage drop corresponding to the density I, across the resistor 21. This voltage is amplified by the high gain amplifier 22 andapplied to the oscilloscope 23 to effect a sweep along the phenomenonaxis corresponding to the density A saw-tooth wave signal Pm ofrelatively low frequency is applied to the drift tube 6 when the switch19 is turned to the contact as shown in FIG. 1, and varies the electronspeed of the electron beam B linearly. As the phase difference 9 betweenthe pulsed electron beam B and the microwave signal P, at the modulationgap It is equal to a sum of the electron transit angle from thephotoelectric surface I to the gap 11 and the phase shift produced bythe phase shifter [7, it is swept over a specific range by the saw-toothwave signal Pm. As easily understood from the drawings of FIG. 2, thesweep of the phase difference results in a sweep of the sampling timepoint t and, therefore, in a variation of the density of the electronbeam passing the pin-hole 14 in accordance with the waveform B to beobserved. Since this variation is applied to the phenomenon axis inputof the oscilloscope and the saw-tooth wave signal Pm is also applied tothe time axis input thereof. the waveform corresponding to the waveformB to be observed is displayed on the display screen of the oscilloscope23.

It is obvious that the sweep of the phase difference 0 can be effectedby directly shifting the phase of the microwave signal P under controlof the saw-tooth wave signal Pm. This can be attained by turning theswitch 19 to the contact 19b to apply the signal Pm to the controlterminal of the phase shifter 17.

As described above, the device of this invention does not need to feedthe sampling voltage pulse to the outside of the envelope E and effectsthe sampling of the waveform to be observed within the vacuum envelopeof an electron tube. Waveform observation can be done in an extremelyhigh frequency range.

Although the above description was made in conjunction with the devicefor observing the waveform of a light pulse, this invention isapplicable to a device for observing the waveform of a high frequencyelectric signal such as microwave signal by providing a suitable unitfor density-modulating an electron beam with this microwave signal.Moreover, by selecting the amplifier 22 and the saw-tooth wave generatoris appropriately, the waveform display can be effected by a mechanicalXY-recorder instead of the cathode-ray tube oscilloscope 23.

I claim:

1. A device for observing a waveform repeated at a high frequency,comprising means of producing an electron beam having a densityvariation according to the waveform to be observed, means for generatinga microwave voltage which is synchronous with the repetition rate of thewaveform to be observed, means for deflecting said electron beam undercontrol of said microwave voltage, means for sweeping the phasedifference between said electron beam and microwave voltage at a lowfrequency, means for collecting said electron beam only at a positioncorresponding to a prede termined deflection effected by said deflectingmeans, and means for displaying the magnitude of the electron flowcollected by said collecting means along the phenomenon axis and saidphase difference along the time axis.

2. A device according to claim 1, wherein said electron beam producingmeans comprises a photoelectric surface formed in an evacuated envelope.

3. A device according to claim 1, wherein said deflection meanscomprises a reentrant cavity resonator to which said microwave voltageis applied.

4. A device according to claim 1, wherein said electron beam collectingmeans comprises a masking electrode having a pin-hole or slit and anelectron collector electrode located behind said pin-hole or slit forcollecting the electrons passing said pin-hole or slit, and said displaymeans comprises a cathode-ray tube oscilloscope, a voltage correspondingto the electron flow collected by said collector electrode being appliedto the phenomenon axis input of said oscilloscope.

1. A device for observing a waveform repeated at a high frequency,comprising means of producing an electron beam having a densityvariation according to the waveform to be observed, means for generatinga microwave voltage which is synchronous with the repetition rate of thewaveform to be observed, means for deflecting said electron beam undercontrol of said microwave voltage, means for sweeping the phasedifference between said electron beam and microwave voltage at a lowfrequency, means for collecting said electron beam only at a positioncorresponding to a predetermined deflection effected by said deflectingmeans, and means for displaying the magnitude of the electron flowcollected by said collecting means along the phenomenon axis and saidphase difference along the time axis.
 2. A device according to claim 1,wherein said electron beam producing means comprises a photoelectricsurface formed in an evacuated envelope.
 3. A device according to claim1, wherein said deflection means comprises a reentrant cavity resonatorto which said microwave voltage is applied.
 4. A device according toclaim 1, wherein said electron beam collecting means comprises a maskingelectrode having a pin-hole or slit and an electron collector electrodelocated behind said pin-hole or slit for collecting the electronspassing said pin-hole or slit, and said display means comprises acathode-ray tube oscilloscope, a voltage corresponding to the electronflow collected by said collector electrode being applied to thephenomenon axis input of said oscilloscope.